ctc12 clone beam current

[timmy]

Originally Posted by DaveWM

the HV adj should not "seem to work" it should work, in a very linear fashion.

Disconnect the pot from the circuit and confirm (preferably with an analog ohm meter) that it is working as it should (500k to near 0 resistance as you adjust).

Confirm the voltage readings at the shunt tube grid and cathode, make sure the grid varies with the pot.

Confirm the total bias of the shunt tube is within specs of the sams.

At some point I recall you saying the HV would go to 30kv with out the CRT anode attached.

If now you are saying the max is 19kv without the CRT attached then only 3 things can be wrong.


Remember you are working with high voltages all over the place (400v around the cathode and grid of the shunt, 30kv at the anode) so be careful.

1) bad shunt tube

2) bad shunt tube bias

3)no loner getting 30kv with shunt tube disconnected.

this set is nuts, lol, lol, the 30kv was with the shunt tube cap off. i have tried 4 shunt tubes all had the same result , no change. as for the voltages at the shunt tube they were where they should be. and 19kv was with the anode wire off the crt. as well as the currant too was ok. i had unsoldered the pot and checked the ohms and again was good.

[DaveWM]

lets break it down

all the following with CRT anode off to take the CRT out of it.

shunt cap off
30kv at anode lead

shunt cap on
19kv to 22kv

HV setting to max

so the shunt is drawing current with pot a the max HV setting

two things can cause it to draw excessive current

1)bad shunt tube (gassy/grid emissions), replace with a KNOWN working one.

2)incorrect bias (voltage divider resistors/pot)
leakying cathode/grid cap on shunt tube (upsetting the bias as well).

It has to be one of the above.

Did you alter any wiring around the shunt? does the cathode resistance to ground change the the HV pot?
do you have resistance checks for the tube pins on the shunt.
did you REPLACE the grid to cathode cap on the shunt? if so did you make sure the replacement cap was good?

[timmy]

Originally Posted by DaveWM

lets break it down

all the following with CRT anode off to take the CRT out of it.

shunt cap off
30kv at anode lead

shunt cap on
19kv to 22kv

HV setting to max

so the shunt is drawing current with pot a the max HV setting

two things can cause it to draw excessive current

1)bad shunt tube (gassy/grid emissions), replace with a KNOWN working one.

2)incorrect bias (voltage divider resistors/pot)
leakying cathode/grid cap on shunt tube (upsetting the bias as well).

It has to be one of the above.

Did you alter any wiring around the shunt? does the cathode resistance to ground change the the HV pot?
do you have resistance checks for the tube pins on the shunt.
did you REPLACE the grid to cathode cap on the shunt? if so did you make sure the replacement cap was good?

ok your right so far but the reg tube i had tried working ones, known working i didnt alter anything at all in the set and the cap i think you are talking about cathode cap i believe it was a disc cap and i got one from moyers but it looked to small even though it was marked as the right one i still had no luck so i found on ebay nos caps and put that one in, was like the original i had changed in the first place. i have the ma specs in earlier posts on the regulator and they appeared ok to a member, it my have been you. you mention voltage divider resistors, where exactly are they? if its the high wattage ones around the hv pot i already did check them. i dont remember if i did resistance checks on the hv reg tube but i do believe i did because i do remember doing all of the others taking awhile to do so. so i dont think i would have left that one out.